*{
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
.tab{
    width: 500px;
    height: 500px;
    margin: 50px auto;
    border: 1px solid #333333;
}

.tab .nav{
    width: 100%;
    height: 55px;
    display: flex;
    align-items: center;
    border-bottom: 1px solid #000;
}
.tab .nav .nav_item{
    flex: 1;
    height: 100%;
    line-height: 55px;
    text-align: center;
    cursor: pointer;
}
.tab .nav .nav_item.current{
    background-color: #000000;
    color: #ffffff;
}

.page{
    width: 100%;
    height: 445px;
    position: relative;
}
.page .page_item{
    display: none;
    width: 100%;
    line-height: 445px;
    text-align: center;
    font-size: 50px;
    position: absolute;
    left: 0;
    top: 0;
    z-index: 20;
}
.page .page_item.current{
    display: block;
}